LS3 Cylinder Head, Cam, and Intake Swap - Crate LS3 Throw Down

Eeking 108 Extra Horsepower out of a Crate LS3 with a Cylinder Head, Cam, and Intake Swap

These days, opting to build a Mouse motor over an LS small-block probably means that familiarity and practicality both stepped into the boxing ring, and the former won via TKO in the 12th round. With all due respect to the legendary Gen I small-block Chevy, from a horsepower-per-dollar standpoint, it just can’t hang with its LS counterpart. Pricier parts and fear factor used to be the biggest strikes against the LS, but that’s no longer the case. Yank a Vortec 6.0L long-block out of junkyard, swap in a mild hydraulic cam, and you’re looking at an easy 500 hp for well under $2,500. With a plethora of carbureted intake manifolds and MSD’s trick LS ignition controller, you can chuck all that EFI—and the fear that comes along with it—right in the trash. While the Gen I small-block Chevy is the most prolific engine ever conceived in terms of sheer production volume and its impact on amateur and professional racing, each successive iteration of the Gen III/IV design reminds enthusiasts why the General jumped ship to a new platform in the first place.

2/16

The proof is in the horsepower. To illustrate the point and test some of the hottest new LS components on the market, we hooked a fresh GM Performance Parts LS3 crate engine to Mast Motorsports’ SuperFlow 902 dyno for a proper WOT christening. While the concept of bolting on a bigger cam, heads, and intake manifold on a crate motor is so cliché in the walk of magazine stories, the results this time around are anything but ordinary. Simply installing a set of Mast’s new 12-degree LS3 cylinder head castings along with a granny-certified 225/231-at-0.050 hydraulic cam netted a gain of 99 hp. That’s not too shabby at all for a naturally aspirated 376 that already puts out 469 hp on stock trim. Throw some more cubic inches and cam into the mix, and the horsepower potential is truly ridiculous.

3/16

The Test Specimen

While the 638hp LS9 and the 505hp LS7 have it handily covered in the power department, the 430hp LS3 used on our dyno session represents the best bang-for-the-buck package in the GMPP crate engine lineup. Currently serving duty in the fifth-gen Camaro SS and the base C6 Corvette, at $6,700 the crate LS3 costs less than half of the price of an LS7. Granted, that’s not exactly pocket change, but it buys a whole lot of motor. Essentially an L92 with a lower profile intake manifold, minus the variable valve timing, the LS3 boasts the same 4.065-inch-bore aluminum block, rectangle-port raised-runner cylinder heads, and 376ci displacement as its Escalade-derived forbear. The combination of a respectable cube’s tally and high-flow heads yield loads of untapped potential, evidenced by the fact that the LS3 produces 430 hp, despite a dinky 204/211-at-0.050 factory cam. Furthermore, the factory’s 430hp rating is quite conservative, as it’s derived using far more stringent SAE testing procedures and correction factor. Under the more conventional Standard Temperature and Pressure standards used by most engine shops, the crate LS3 actually produced 469 hp and 465 lb-ft on Mast Motorsports’ dyno.

4/16

Camming Up

The phenomenal airflow capabilities of the Gen III/IV cylinder heads, and GM’s need to keep its cam specs conservative for streetability and emissions purposes, means that tremendous performance gains can be had by simply upgrading to a larger camshaft. Late-model enthusiasts realized this about two days after the first LS1s hit the showroom, but the odds are stacked in favor of hot rodders even more with the LS3. That’s because the 376ci LS3 uses the same camshaft as in the 346ci ’01 LS6, albeit with a smidgen more intake lift. Furthermore, the LS3’s rectangle-port cylinder heads flow roughly 60 cfm more than the cathedral-port LS6 castings (260 versus 320). Considering that its factory cam was originally designed for an engine that’s 30ci smaller and heads that flow 60 fewer cfm, it’s not surprising that the LS3’s torque curve plummets rapidly after 4,700 rpm. To remedy the situation, Mast installed one of its 225/231-at-0.050 hydraulic cams in our test subject, which features 0.602/0.607-inch lift and a 115-degree lobe-separation angle.

5/16

Call the specs girlie if you must, but it’s tough to find fault with a 64hp gain we witnessed on the dyno, bringing the grand total to 533. That’s right, folks, 533 hp from an otherwise-stock LS3 with nothing more than a cam swap. Examining the dyno sheet reveals that the Mast cam effectively moved peak torque up to 480 lb-ft at 5,400 rpm compared to the stocker’s 465 lb-ft at 4,700 rpm. While the Mast cam only yielded an additional 15 lb-ft, moving the torque peak higher up on the powerband boosted peak power big time. The cam did give up some grunt below 3,000 rpm, but after that it produced 400 lb-ft of torque or more all the way up to 6,200 rpm. Mast attributes this remarkably broad powerband, in part, to the cam’s wide 115-degree LSA. “The stock LS3 heads flow so much air that you don’t need a ton of duration to make lots of power,” Horace Mast, of Mast Motorsports, explains. “This cam was designed for a stock displacement engine, and our goal is to increase power while retaining smooth idle quality and OE driveability. We also offer a slightly larger 230/237-at-0.050 cam that makes an extra 8-10 hp.”

Head Swap

Without question, the biggest aces up the LS3’s cylinder sleeves are its outstanding factory heads. These 260cc castings borrow their basic architecture from the LS7 heads, utilizing raised rectangular intake ports and monster 2.165/1.590-inch valves. With 320-330 cfm of flow right out of the box, they can easily support 600 hp. As great as the stock LS3 heads may be, Mast says that their brand-new castings blow them away by 40-50 cfm on the flowbench. To see if those bold claims actually held true on the dyno, we had to test them out.

Mast’s all-new CNC-ported castings sell for $3,600 fully assembled, and feature 256/89cc ports, 2.165/1.600-inch valves, and 69cc combustion chambers. Those critical dimensions are similar to stock, but Mast says that flattening out the valve angle from 15 to 12 degrees and revising the port geometry gives its heads a substantial increase in flow. Despite repositioning the valves, the heads are fully compatible with stock pistons. On a 4.070-inch bore fixture, Mast advertises 351 cfm at 0.600-inch lift, and 370 cfm at 0.700-inch lift on the flow bench. Once bolted to the crate LS3, the Mast heads lived up to the hype. Output jumped to 568 hp and 507 lb-ft for gains of 35 and 27 numbers, respectively, over the stock hardware. Last we checked, 507 lb-ft of torque from a 376ci motor—which works out to 1.34 lb-ft per cubic inch—is stout by any measure, a testament to how efficiently the Mast-modified LS3 fills its cylinders with air.

Mast Medium-Bore LS3 Heads

Lift

Intake

Exhaust

0.100

77

56

0.200

148

118

0.300

237

165

0.400

295

208

0.500

328

227

0.600

351

235

0.700

370

241

More Inches, Please

Although a 99hp gain with a cylinder head and cam swap is mighty impressive, unless you’re willing to turn 7,500-plus rpm, a 376ci short-block is far too small to take advantage of 370 cfm of airflow. To demonstrate the potential of the Mast heads, given more cubes and cam, we bolted them up to a 416ci stroker short-block and matched it up with a 242/260-at-0.050 cam ground with 0.615/0.642-inch lift and a 114-degree LSA. Essentially a stroked LS3, it’s comprised of a 6.2L block bored 0.005-inch over, a Callies 4.000-inch forged crank and rods, and 11.2:1 Mahle pistons. The enlarged short-block did bump up compression a half-point over the stock LS3, but it’s safe to assume that the majority of the gains were attributable to the extra cubes and more aggressive cam. The final dyno tally registered 630 hp and 555 lb-ft of torque for an increase of 62 and 48 numbers, respectively. Just imagine what this puppy would do with another 20 degrees of cam duration.

Parts List

Item

PN

Price

GMPP LS3 crate engine

19201992

$6,675

Mast cam and valvesprings

963-102

$680

Mast cylinder heads

510-202

$3,675

15/16

The Mast camshaft gives up some torque down low, but catches up to the stock cam by 3,000 rpm. The difference in area under the curve is substantial after 4,700 rpm, where the stock cam drops off sharply, and the Mast unit pulls hard up to 7,000 rpm.

16/16

Bolting the Mast cylinder heads onto the cam’d LS3 crate motor produced a linear gain in power from 2,000-7,000 rpm. According to Mast, the company’s brand-new heads are good for 25-30 hp over its CNC-ported stock LS3 castings in its crate engine packages.

Sources

MORE PHOTOS

VIEW FULL GALLERY

xclose

LS3 Cylinder Head, Cam, and Intake Swap - Crate LS3 Throw Down

GMPP currently offers three different variants of the LS3 in crate trim. In addition to the base LS3 used in our test, it’s also available with a larger 219/228-at-0.050 cam that boosts output to 480 hp and 475 lb-ft. Dubbed the LS 376/480 (PN 191712240), it costs the same as a base LS3. For an extra $600, GMPP matches up a larger 226/236-at-0.050 cam with a single-plane intake manifold to create the LS 376/515 (PN: 19171225), which increases performance to 515 hp.

Like many modern camshaft designs, the Mast unit packs steep ramps onto its billet core with 0.602/0.607-inch lift spread over a rather tame 225/231 degrees of duration at 0.050 lift. This allows taking advantage of the high-lift flow numbers of the LS3 heads without sacrificing streetability. Since the cam was designed primarily for EFI applications, its wide 115-degree LSA enhances engine vacuum and smooths out idle quality.

Along with the cam swap, Mast installed its nitrided 1.290-inch springs onto the stock LS3 heads to handle the extra valve lift. They feature 130 pounds of seat pressure, 318 pounds over the nose, and are good for up to 0.650-inch lift. The springs are direct stock replacements that are compatible with the stock retainers and locks, and are sold as a package with the Mast cam for $680.

Mast’s LS3 head castings are available in three different trim levels for small- (3.900 to 3.930), medium- (4.000 to 4.070), and large-inch bore (4.125 to 4.200) motors. The small-bore heads have 253/89cc ports and 2.080/1.600-inch valves, the medium-bore heads utilize 256/89cc ports and 2.165/1.600-inch valves, and the large-bore heads offer 270/87cc ports and 2.200/1.600-inch valves. Prices for a fully assembled set—which includes factory GM rocker arms and Mast rocker stands—start at $3,600. That’s not cheap, but there’s no denying the tremendous volume of air they move.

The ports and combustion chambers on the Mast heads are fully CNC machined prior to shipment. Flatting out the valve angle from 15 to 12 degrees not only helps de-shroud the valves, but it also yields a smaller, more efficient, and faster-burning combustion chamber design. Customers have the option of choosing between solid- and hollow-stem steel valves, and our test heads were fitted with the latter.

Although airflow could have been increased significantly by raising the intake ports to complement the flatter valve angle, Mast opted to leave them in the stock location to maintain compatibility with factory intake manifolds. Mast’s small-, medium-, and large-bore heads flow 353/257, 370/241, and 390/249 cfm, respectively, at 0.700-inch lift. Those figures were achieved using appropriately sized 3.900-, 4.070-, and 4.125-inch bore fixtures for each trim level of head.

Compared to the stock LS3 cylinder heads (left), the Mast castings have a much thicker 0.750-inch deck to prevent distortion in power adder applications. Optional are two extra stud bosses cast into the 12 o’ clock and 6 o’ clock positions around each cylinder, making them compatible with six-bolt aftermarket blocks. The valve cover rails have also been increased in height for extra rocker arm clearance.

The thicker decks of the Mast heads require longer 8.150-inch pushrods. Mast offers its own chromoly units, which are 3/8 inch in diameter with 0.080-inch wall thickness. Our test heads were fitted with titanium retainers.

Stock L92/LS3 rocker arms can be used on Mast’s cylinder heads, but they must be bolted to an aluminum rocker stand in order to line up with the repositioned valve location. Like the LS7, the LS3 incorporates offset intake rockers to minimize pushrod pinch. However, LS7 and LS3 rockers are slightly different and are not interchangeable.

Just for fun, we bolted up a Performance Inductions single-plane intake manifold onto the stock LS3 short-block along with a Pro Systems 750-cfm carb. The combo clearly needed more cam and rpm to truly shine, as it picked up 9 hp over the stock LS3 intake but sacrificed 43 lb-ft in the process. Mast says that the single-plane manifold could easily crack the 600hp mark if matched with an appropriately sized cam.

As no surprise, matching the Mast heads up with a bigger 416ci short-block and 242/260-at-0.050 cam really woke them up, boosting output to 630 hp. With a big-block-like 370 cfm on tap, they can easily support 500 ci, proof once more that today’s cylinder heads can feed as many cubic inches as you can realistically throw at them.

In addition to its line of handbuilt stroker motors, Mast also carries the full line of GMPP crate engines. Mast offers stock LS3s, L92s, and L99s as turnkey packages by installing its cam and valvespring upgrades in them, then matching them up with a Mast stand-alone computer, a wiring harness, a starter, and a water pump. The Mast-modified crate LS3 used in our dyno test sells for $12,995.CHP

The Mast camshaft gives up some torque down low, but catches up to the stock cam by 3,000 rpm. The difference in area under the curve is substantial after 4,700 rpm, where the stock cam drops off sharply, and the Mast unit pulls hard up to 7,000 rpm.

Bolting the Mast cylinder heads onto the cam’d LS3 crate motor produced a linear gain in power from 2,000-7,000 rpm. According to Mast, the company’s brand-new heads are good for 25-30 hp over its CNC-ported stock LS3 castings in its crate engine packages.